Reading this post reminded me of a Q&A I recently read in a Southenr Ponds and Wildlife magazine. A writer asked the author of the mag (owner of American Sportfish in Montgomery AL)"How is the best way to keep brush from growing around the pond banks without harming the fish?" The response was:

Spray the brush in the spring or early summer with Arsenal or Roundup. You can spray all the way down to the edge of the water. these materials are not toxic to fish."

According to the first post in this thread, round up is harmful to amphibians. What about fish?